This invention relates to fluid actuators, and is more particularly concerned with a device that converts a fluid pressure to a tensive force, e.g., to exert a pull on a control cable or the like. The invention is more specifically directed to a terminator for a distal end of a hydraulic muscle that seals the end of an elongated bladder of the muscle, provides mechanical transfer of force from a braid of the muscle to the control cable or other mechanical device, and permits air or other gases to be bled from the bladder.
The invention can also be incorporated into a hydraulic pump which operates on the same principle as the hydraulic muscle.
Hydraulic muscles can favorably be employed within a borescope or endoscope to control the steering or bending at the distal tip, and to avoid the need for extremely long steering cables.
A borescope is generally characterized as an elongated flexible insertion tube with a viewing head at its distal or forward end, and a control housing at its proximal end for controlling or steering the distal or forward end. Such a borescope has a bendable-tube steering section or articulation section at the distal end adjacent the viewing head. One or two pairs of control cables extend through the articulation section, and then through the remainder of the flexible insertion tube. These cables connect with a steering control unit in the control section. One or both pairs of these cables are differentially displaced to bend the articulation section. The viewing head can thus be remotely oriented to facilitate the inspection of an object. Borescopes are intended for visual inspection of mechanical devices such as jet engines or turbines, where it would be difficult or impossible to examine the device's internal elements directly. The borescope needs to reach into narrow tortuous passageways, and must observe similar bending and steering considerations. In addition the pathway to the object can be quite long, and so it is often necessary that the borescope insertion tube be fifteen meters or longer.
Endoscopes are similar devices, but are intended to be inserted into a body cavity, such as the colon or esophagus, for visual investigation of tissues within the cavity.
A number of types of cable-actuated articulation or steering mechanisms are known, and typical ones are discussed in U.S. Pat. Nos. 3,610,231; 3,739,770; 3,583,393; 3,669,098; 3,779,151; and 4,347,837. Another steering mechanism is described in U.S. Pat. No. 4,700,693.
The articulation mechanisms for those previously-proposed endoscopes and borescopes require that the cables have a significant amount of slack or play because bends and coils in the insertion tube effectively shorten the cables and because the articulation section bends at discrete points rather than following a smooth curve. However, in both the borescope and endoscope, the articulation section must be bent rather precisely to penetrate into the area to be inspected without damaging delicate engine parts or injuring a patient's tissues. For these reasons cable tension must be limited and cable slack must be minimized. Where the insertion tube is long, extra cable slack is often included to accommodate the increased cable tightening due to the substantial coiling and bending of the insertion tube through which the steering cables pass.
Also, when the cables are differentially displaced to effect articulation, the cable displacement is not precisely reciprocal. That is, the motion of one cable is not the exact opposite of the other. This fact results in undesirable tensioning at some times, and at other times produces unwanted cable slack which can lead to imprecise steering. Coiling of the insertion tube can produce high tension in both cables of a cable pair, which can lead to increased friction and to high damaging forces on the cables and on the articulation section. If no measures are taken to compensate for this, early failure can follow. Even when only one cable carries tension, coiling of the insertion tube can produce sufficient friction on the cable to prevent articulation.
Ideally, the steering cables should be kept short to avoid the above problems. To do this, the cables should terminate within the insertion tube near the articulation section, and some mechanism to draw the cables should be incorporated within the sheath of the insertion tube. Unfortunately, no known existing mechanism had been proposed for this task until U.S. Pat. No. 4,794,912. This patent describes a braid-and-bladder pneumatic or hydraulic muscle that addresses many of the problems found in these prior borescope/endoscope steering mechanisms. Specifically, a fluid dynamic muscle mounted adjacent the distal end of the insertion tube is actuated by pneumatic or hydraulic pressure supplied through small flexible tubes within the borescope insertion tube. The muscle is mounted adjacent the flexible portion of the endoscope/borescope so that the bending cables can be very short and direct in the performance of their bending function without the limitations and problems of the much longer cables required in the conventional steering mechanisms. As fluid pressure is applied to the fluid muscle situated in the distal end of the borescope, the insertion tube bends in the desired direction to permit proper viewing. The problems of extremely long cables that flex, stretch, etc. are avoided. This allows a much more accurate and precise positioning of the viewing end of the borescope within the cavity being inspected.
Where longer distances are encountered from the fluid pressure source to the muscles, a hydraulic or liquid driven system is preferred because of the increased control and decreased response times. However, in such case it is essential to provide a highly reliable seal at the ends of the muscle bladder. It is also important to provide a bleed port through which air or other gases trapped in the bladder during fabrication can be removed from the hydraulic muscle.